Method and apparatus for metal rolling



Dec. 22, 1964 McLAY ETAL 3,162,069

METHOD AND APPARATUS FOR METAL ROLLING Filed Oct. 27, 1961 3 Sheets-Sheet 1 54 FIGJ SCREWDOWN CONTROL w w 4 DEVIATION 5g 15 DEV|A1|ON GAGE 38 I I 40 GAGE I as k. :82 86 88 MOTOR CONTROL so |O8-4LAMPLIFIER 5/ P82 E? INVENTORS I02 S PL ATTENUAT'ON "7/ Alexander McLoy 8| a Eugene Aweremeychik LAG NETWORK BY A OR YS Dec. 22, 1964 Filed Oct. 27. 1961 3 Sheets-Sheet 28 54 SCREWDOWN CONTROL 3:; Q

24 sex ,52 DEVIATION 46 48 DEVIATION GAGE ea ,as MOTOR MOTOR CON"ROL CONTROL [I30 TMAGNETIC AMPLIFIER INVENTORS Alexander McLuy 8 Eugene A.Weremeychik Dec. 22, 1964 MCLAY ETAL 3,162,069

METHOD AND APPARATUS FOR METAL ROLLING Filed Oct. 27, 1961 5 Sheets-Sheet 3 |s2 SWITCH SCREWDOWN 28 3 2o CONTROL FIG.

we L DEVIATION f 5 DEVIATION GAGE "1 f GAGE ,68 ,aa MOTOR MOTOR CONTROL CONTROL 70 T90 SWITCH I36 1'' us POWER SUPPLY no n2 10s 12 H4 7 I 2 I047 ATTENUATION '20 a AMPLIFIER LAG NETWORK k SWITCH 134 INVENTORS United States Patent Ofiice altars Patented Dec. 22, 1964 3,162,tl69 rvmrnon APPARATUS non s/mTAL RULLHNG Alexander Malay, Leechburg, and Eugene A. Weremeychili, Brackenridge, Pan, assignors to Allegheny Ludlum Steel Corporation, Breckenridge, Pin, a corporation of Pennsylvania Filed Oct. 27, 1961, Ser. No. 148,087 9 Claims. (Cl. 80-32) This invention relates in general to the art of metal rolling, and more particularly to the art of cold reducing metal strip by the conjoint action of pressure on the reducing rolls of a mill and tension on strip material passing through the mill. Although the invention is particularly adapted for use with a mill of the 4-high type, it may also be used with cluster, Sendzimir or other types of mills.

In cold reducing metal strip, it is common to employ forward tension and back tension on the metal passing through the work rolls of the mill. In a mill of the 4-high type, for example, there: are two work rolls which are backed up by backing rolls having a relatively large diameter as compared with the diameter of the work rolls. Such mills may be employed as single stand mills or arranged in tandem. Power is commonly supplied to the mill by driving the backup rolls which, in turn, drive the work rolls by frictional engagement therewith, or by driving the work rolls directly. Additionally, power is often supplied through tension on the delivered strip, this tension being imparted to the delivered strip by means of a motor-driven tension reel.

In conjunction with the forward tension mentioned above, cold rolling of metal strip usually involves the use of back tension or drag on the strip to assist in reducing the thickness of the product, particularly where fine gage tolerances are required. The back tension is usually supplied by an unwinding reel provided with some type of braking means such as a motor-generator which acts as a generator during the unwinding of the strip to produce the desired amount of tension.

The thickness of the strip is determined primarily by the spacing between the work rolls; and this spacing, in turn, is adjusted by means of a conventional mill screwdown. Thus, if it is desired to roll strip to a thickness of 0.025 inch, for example, the screwdown is adjusted for the proper spacing of the work rolls; but since the entering strip material varies in thickness along its length, the material leaving the mill will also vary above and below 0.025 inch. Accordingly, in order to produce a constant thickness along the length of the strip, the spacing between the work rolls, the back tension, the forward tension, or combinations of these must be continually varied as the thickness of the entering strip changes. While exit thickness can be controlled by adjusting the mill screwdown, perfect gage control can probably best be obtained by controlling the tension in the strip, and particularly the back tension. I

In the past, the back tension was commonly controlled from a gage measurement taken several feet beyond the exit side of the mill. In a system of this sort the material, after reduction, progressesto the gage which may be several feet beyond the bite of the roll before any error present in the material thickness can be detected. This distance from the bite of the rolls to the gage is commonly referred to as transport distance. The time required for the material to reach the exit gage is denoted as transport time, while the time required to measure the strip gage is referred to as sensing time. Transport time and sensing time are major elements in developing error commands. Transport distances of five feet or more are common in most commercial rolling equiment available at present, meaning that such a system is not capable of detecting an error signal until five feet of material has passed from the bite of the mill working rolls. The corrective signal is then transmitted to the generator on the unwinding reel; but the measuring gage does not detect the result of this action until five feet more of the material have passed through the mill. The result is that only rough tolerances in the gage of the strip can be obtained, a variation of plus or minus 10% in gages of 0.025 inch, for example, being common.

As an overall object, the present invention seeks to provide a method and apparatus for rolling metal strip material to within fine tolerances by controlling the tension in the strip being rolled.

More specifically, the invention relates to :a method and apparatus for controlling the gage of cold reduced metal strip by varying back tension, forward tension or both as a function of the exit gage of strip material leaving the bite of the working rolls of the mill.

Still another object of the invention is to provide a gage control system for rolling mills wherein the gage is controlled at the bite of the rolls.

in accordance with the invention, metal strip to be rolled is passed between the working rolls of a mill and placed under tension by means of braking applied to an unwinding reel or the like. In contrast to prior art rolling mill systems wherein an attempt is made to hold the back tension constant or to change the tension in relation to the thickness of the strip material leaving the mill, the present invention provides a system wherein back tension is controlled by measuring incoming gage on the mill and generating corrective signals which are applied to the back reel regulators or braking means. The invention thus eliminates the undesirable feature of prior art systems which measure gage after the fact rather than before the fact. That is, whereas prior art systems are not capable of detecting an error signal until the material has passed from the bite of the rolls, the present invention detects the error signal before the material passes to the bite of the rolls. By delaying the application of this error signal to the tension reel regulator or braking means by an amount equal to the time required for the material to travel from the gage to the bite of the rolls, the back tension on the strip may be made to vary as a function of the gage of the material directly at the bite of the rolls rather than the gage of material after it has passed from the bite of the rolls as in prior art systems. It has been found that whereas gage tolerances of plus or minus 10% are common with prior art systems, the present invention provides for gage tolerances of only plus or minus about 1.5%.

in the usual mill installation, two gages are provided, one at the entrance side of the working rolls and the other at the exit side. The gage at the entrance side produces error signals for controlling back tension; whereas the gage at the exit side is employed to control the mill screwdown in a conventional manner. Although incoming gage measurements are possibly best utilized by varying the back tension on the strip, they can also be used for varying forward tension or a combination of forward and back tension as will hereinafter be seen from a consideration of specific embodiments of the invention.

The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings which form a part of this specification, and in which:

FIGURE 1 is a schematic illustration of one embodiment of the invention for controlling back tension and/ or forward tension by measurement of input gage;

PK 2 is a. schematic illustration of another embodiment of the invention; and

FIG. 3 is an illustration of an embodiment of the invention as applied to a reversing cold rolling mill.

Referring now to the drawings, and particularly to FIG. 1, there is shown a single stand cold rolling mill having an outer housing 1% which supports an upper work roll 12 and a lower work roll 14. The upper work roll 12 is in frictional engagement with and is backed up by a backing roll 16 having a much larger diameter than the working roll 12. Similarly, the work roll 14 is backed up by and in frictional engagement with a backup roll 18 of large diameter. The rolls 16 and 18 are driven by motors 20 and 22, respectively; and the work rolls 12 and 14 are, in turn, driven by frictional engagement with rolls 16 and 18. The spacing between the work rolls l2 and 14 is controlled by means of a screwdown mechanism 24 which, in turn, is connected through shaft 26 to an electrical screwdown control 28.

In the particular illustration given, the material 30 to be rolled comprises a continuous strip which feeds off payoff reel 34 and is coiled onto take-up reel 36, the direction of strip travel being as indicated by the arrows. In passing from reel 34 to reel 36, the strip material 3t) passes between the work rolls 12 and 14 which effect a reduction on the material. As will be understood, the direction of movement of the strip material through the mill may be reversed, whereupon the reel 3:6 will become the payoif reel and reel 34 will become the take-up reel.

Positioned on either side of the mill are a pair of gage heads 38 and 40, each of which supports a vertically movable roller 42 positioned above the strip and a fixed roller 44 below the strip. Connected to the vertically movable rollers 4-2 through linkages 4-6 and 48 are electronic deviation gages 56 and 52 which are adapted to produce electrical output signals which vary as a function of the deviation in gage of strip 30 from a predetermined gage. For a full and detailed description of one type of specific deviation gage which may be used herein, reference may be had to US. Patent No. 3,140,545, issued July 14, 1964 andassigned to the assignee of the present application. For purposes of this description, however, it may be said that any device will sufiice for gages i? and 52 which will produce an electrical output signal which varies as a function of the deviation in gage of strip 30 from a predetermined value.

The output of gage 52 is applied through leads 54 to the screwdown control 28; and in this manner the screwdown is controlled by means of the exit gage of strip material leaving the work rolls 12 and 14 in accordance with usual practice.

Referring now to the unwinding reel 34, it is connected through mechanical linkage 56 to the armature 58 of direct current motor-generator apparatus 59. As shown, the armature 58 is connected through a series Winding 60 to a direct current generator 62 driven by a motor 64. However, when reel 34 acts as an unwinding reel, the armature 58 will act as the armature of a generator which, in turn, will drive generator 62 as a motor, thereby providing the necessary drag or back tension on reel 34.

Magnetically coupled to the armature is a field winding 66 which is controlled by means of motor control circuit 68. The current through winding 66 is, in turn, controlled by means of a manually adjustable rheostat 7 t) and a second rheostat 72 connected in series therewith. As shown, rheostat 72 is connected through mechanical linkage 7 4 to a servomotor 7 6 having two phases or windings 78 and se thereon.

In a similar manner, the winding reel 36 is connected through mechanical linkage 82 to the armature 84 of motor-generator apparatus 85 having a field winding 86 connected to a motor control circuit 88. In this case, the current through field winding 86 may be controlled by means of a single manually adjustable rheostat 99 when switch 91 is in the position shown. Alternatively, the rheostat 90 may be connected in series with a second rheostat 93 which, like rheostat 72, is connected through linkage 74 to servomotor 7e. Armature 84 is connected through series winding 92 to a generator 94, this generator being mechanically connected to motor 96. Since reel 35 acts as a Winding reel, the armature $4 acts as the armature of a motor which is driven by the generator 94 to apply a forward torque to reel 36 and thereby provide the desired amount of forward tension to strip 36.

Referring now to deviation gage 58, its output is applied across series-connected resistors 8 and 1%. The voltage across resistor 1% is applied through movable tap 102 to an attenuation and lag network 104 which delays the signal from deviation gage 59 in an amount substantially equal to the time required for the strip 3%) to travel from gage rollers 4-2 and 44 on the input side of the mill to the bite of rolls l2 and l t. Thus, when the signal arrives at the output of circuit 164, it will represent the gage of entering strip material directly at the bite of the rolls. The output from circuit 1% is applied through a bridge circuit ms to an amplifier 138. The bridge circuit 106 comprises a first pair of resistors 110 and 112 which function as two of the four impedances of the bridge circuit, and a potentiometer 1E4 having its movable tap 116 connected to the input of amplifier 168. In this manner, the resistance of the potentiometer on either side of the movable tap 116 comprises the other two of the four impedances of the bridge circuit. Current is supplied to the bridge circuit from voltage source 117 through rheostat 118.

Amplifier 1% in connected to a source of alternating current voltage 129, this voltage source also being applied to winding 78 of the servomotor 76 as a reference voltage. The output of amplifier 168 is applied to the other winding as of the servomotor 76; and the signal across winding $9 is compared with that across winding 78 to rotate the servomotor 76 in one direction or the other. As shown, servomotor 76 is connected to both the movable tap 116 on rheostat 114 in bridge circuit 106 as well as the movable taps 122 and 123 on rhesostats 72 and 93, respectively, in the control circuits for shunt windings 6d and 86.

In the operation of the system, it will be assumed initially that switch 91 is in the position shown so that rhcostat 9b is disconnected from rheostat 93. Under these circumstances, forward tension can be controlled only by manually rotating the tap on rheostat 99. If the gage of the entering strip material 30 is that gage to which the deviation gage 50 is set, the bridge circuit 1% will be balanced, and the servomotor 76 will be stationary. If, however, the gage of the entering strip 39 should exceed the predetermined gage to which the gage 50 is set, then the bridge circuit 1% will become unbalanced, and the servomotor 76 will be rotated to rotate tap 116 until the bridge is again balanced. At the same time, the tap 122 on rheostat 72 will be rotated to change the field current through winding 66, thereby changing the back tension on reel 34. As the gage of entering strip material increases above the predetermined gage, the back tension will be increased for the increase in gage. If, on the other hand, the gage of entering strip material should fall below the aforesaid predetermined gage, the bridge circuit 166 will again become unbalanced, but in this case the servomotor will be rotated in the opposite direction until the bridge 1% is again balanced. In this process, the tap 122 on rheostat 72 is rotated in the opposite direction, thereby Varying the field current through winding 66 to decrease the back tension on reel 34. It can thus be seen that as the gage of entering strip material varies above and below the aforesaid predetermined gage, the back tension on reel 34- will be varied a corresponding amount to compensate for the variation in gage.

As was mentioned above, the variation in gage can be compensated for by varying the back tension, the forward tension, or both. Both back tension and forward tension may be varied by reversing switch 91 such that the rheostat associated with motor control circuit 88 is connected in series with rheostat 93. Now, as the servomotor 76 rotates in one direction or the other in response to gage variations on the input strip 30, both of the taps 122 and 123 will be rotated to vary the field current through windings 66 and 86, the result being that both the back tension on reel 34 and the forward tension on reel 36 are increased or decreased to compensate for variations in gage. Regardless of whether rheostat 93 is switched into or out of the circuit, the network 104 serves an important function in that it damps the signal applied to the bridge circuit 196 and also delays the signal by an amount of time equal to the time required for the strip to travel from rollers 42 and 44 on gage head 38 to the bite of rolls 12 and 14. Thus, the instantaneous signal controlling rheostat 72, or both of the rheostats 72 and 93, is that representing the gage directly at the bite of the rolls. With this type of control, extremely fine tolerances in gage can be maintained. For example, in an actual test employing the system of the invention, seven small strips were cut from a larger coil which had been passed through a rolling mill in which back tension alone was controlled from input gage measurements in accordance with the system of FIG. 1 (i.e., switch 91 was in the position shown to disconnect rheostat 93 from circuit 83). The strips ranged in length from 108 inches to 156 inches at a nominal gage of 0.025 inch. Readings taken at every six inches along the length of the strips showed that the maximum gage variation in any one strip was 0.00020 inch and that the maximum gage variation along all seven strips was 0.00035 inch. This, of course, is an amazingly high degree of accuracy unattainable with prior art systems of the type described above.

In FIG. 2 another embodiment of the invention is shown wherein elements which correspond to those shown in FIG. 1 are identified by like reference numerals. In this case, however, the output signal from deviation gage 5'0 is applied through a magnetic amplifier 130 to the control circuit for winding 66. The magnetic amplifier 13d effectively replaces the servo system and rheostat 72 of FIG. 1 in the control circuit and cooperates with rheostat 70 to control the current through field winding 66 and, hence, the back tension in reel 34. As will be understood, the output from magnetic amplifier 130 could also be used to control the current through field winding 86 and, hence, the forward tension produced by reel 36, if desired.

In FIG. 3 still another embodiment of the invention is shown for a reversing-type mill wherein the reels 34 and 36 alternately act as unwinding and winding reels, depending upon the direction of strip movement through the mill. In this case, three switches 132, 134 and 136 are required. Switch 132 serves to apply the output from either deviation gage 50 or 52 to screwdown control 28, depending upon the direction of strip movement through the mill. Thus, when the strip moves from left to right as shown in FIG. 3, the switch 132 will apply the output from gage 52 to the screwdown control 28 since this gage gives an indication of the deviation in output gage of the strip. Conversely, when the direction of strip movement through the mill is reversed so as to be from right to left, switch 132 will apply the output of deviation gage 5% to screwdown control 28 since this now represents deviation in output gage of the strip.

Switch 134 acts in an opposite manner to switch 132 in applying the output of the deviation gages and 52 to resistors 98 and 1%. Upon movement of the strip material 39 from left to right, the output of gage 5d is applied to the resistors 98 and 100; whereas when the strip moves in the opposite direction, the switch 134 applies the output of gage 52 to resistors 98 and 1109. Switch 136 serves to connect the control circuit 68 or 88 to the rheostat 72, the arrangement being such that upon movement of the strip material from left to right, switch 136 will connect rheostat 72 to control circuit 63 since reel 34 is now acting as an unwinding reel. Conversely, when the direction of strip material through the mill is reversed, the switch 136 will disconnect the rheostat 72 from motor control circuit 68 and connect it to control circuit 88 since reel 36 is now acting as an unwinding reel. As will be understood, the system of FIG. 3 could be modified such that both of the reels 34 and 36 are controlled in response to variations in gage, thereby eliminating the switch 136.

Although the invention has been shown in connection with certain specific embodiments, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

We claim as our invention:

1. In rolling mill apparatus of the type having a pair of work rolls through which strip material to be rolled passes and mechanism for producing back tension in the strip material during rolling, the combination of a device for producing an electrical signal which varies in direct proportion to gage the strip material before it passes between the work rolls, and apparatus operatively connected to said device and responsive only to the electrical signal produced by said device for controlling said mechanism whereby the back tension in the strip will vary in direct proportion to the gage of strip material entering the work rolls.

2. In rolling mill apparatus of the type having a pair of work rolls, an unwinding reel for strip material to be rolled between the work rolls, and electromotive means on the unwinding reel for producing back tension in the strip material during rolling; the improvement of gage means for producing an electrical signal which varies in direct proportion to the deviation in thickness of the strip material entering the Work rolls from a predetermined value, and means connected to said gage means for controlling the electrornotive means on the unwinding reel whereby the back tension will vary in proportion to variations in said electrical signal.

3. In rolling mill apparatus of the type having a pair of work rolls, screwdown means for adjusting the spacing between said work rolls, an unwinding reel for strip material to be rolled between the work rolls, and electrornotive means on the unwinding reel for producing back tension in the strip material during rolling; the improvement of first gage means for producing a first electrical signal which varies in direct proportion to the deviation in thickness of the strip material entering the work rolls from a predetermined value, second gage means for producing a second electrical signal which varies in direct proportion to the deviation in thickness of the strip material leaving the work rolls from a predetermined value, means connected to said first gage means and responsive only to said first electrical signal for controlling the electromotive means on the unwinding reel whereby the back tension will vary in proportion to variations in the first electrical signal from said first gage means, and means connected to said second gage means for controlling the screwdown means whereby the spacing between the work rolls Will vary in response to variations in the second electrical signal from said second gage means.

i 4. In rolling mill apparatus of the type having a pair of work rolls, an unwinding reel for strip material to be rolled between the work rolls, and electrornotive means on the unwinding reel for producing back tension in the strip material during rolling; the improvement of gage means positioned between the unwinding reel and the work rolls for producing an electrical signal which varies in direct proportion to the deviation in thickness of the strip material from apredetermined value, and means including a delay network for applying only the electrical signal produced by said gage means to said electrornotive means whereby the back tension produced by the electrornotive means will vary in proportion to said electrical signal.

S. In rolling mill apparatus of the type having a pair of work rolls, screwdown means for adjusting the spacing between said work rolls, an unwinding reel for strip material to be rolled between the work rolls, andelectromotive means on the unwinding reel for producing back tension in the strip material during rolling; the improvement of a first gage positioned between the unwinding reel and the work rolls for producing a first electrical signal which varies in direct proportion to the deviation in thickness of the strip material entering the work rolls from a predetermined value, a second gage positioned on the side of said work rolls opposite said first gage for producing a second electrical signal which varies as a function of the deviation i'n'thickness of the strip material leaving the work rolls from a predetermined value, means for applying said first electrical signal aloneto said electromotive means for controlling the same whereby the back tension on said strip material will vary in proportion to the gage of strip material entering the work rolls, and means for applying said second electrical signal to said screwdown whereby the spacing between said work rolls will vary as a function of the gage of strip material leaving the work rolls.

6. In combination, rolling mill apparatus having a pair of work rolls, an unwinding reel for strip material to be rolled between the work rolls, electromotive means operatively connected to the unwinding reel for producing back tension in the strip material, said electromotive means including anarmature coupled to said unwinding reel and a field winding for the armature, a gage positioned between said unwinding reel and said work rolls for producing an electrical signal which varies in direct proportion to the gageof strip material entering said work rolls, and apparatus including magnetic amplifier means connected to said gage for controlling the current through said field winding in proportion to variations in said electrical signal whereby the back tension produced by the electromotive means will vary as a function of the gage of strip material entering said work rolls.

7. The method for reducing metal in strip form in a mill having a pair of work rolls, which comprises positioning the strip between the work rolls and driving the work rolls while forcing the work rolls together to roll the strip, applying back tension on the strip during the rolling operation, and electrically controlling said back tension in direct proportion to the gage of strip entering the bite of the work rolls.

8. The method for reducing metal in strip form in a mill having a pair of work rolls and screwdown means for adjusting the spacing between said work rolls, which comprises positioning the strip between the work rolls and driving the work rolls while forcing the work rolls together to roll the strip, applying back tension on the strip during the rolling operation, electrically controlling said back tension in direct proportion to the gage of strip entering the bite of the work rolls, and electrically controlling said screwdown as a function of the gage of strip leaving the bite of the work rolls.

9. The method for reducing metal in strip form in a mill having a pair of work rolls, which comprises positioning the strip between the work rolls and driving the work rolls while forcing the Work rolls together to roll the strip, applying back tension on the strip during the rolling operation, and electrically controlling said back tension in direct proportion to the deviation in gage of strip entering the bite of the work rolls from a predetermined gage.

References Cited in the file of this patent UNITED STATES PATENTS Re. 25,075 Hessenberg Oct. 31, 1961 2,105,431 Mohler et al Ian. 11, 1938 2,281,083 Stoltz Apr. 28, 1942 2,883,895 Vossberg Apr. 28, 1959 3,054,311 Murtland Sept. 18, 1962 3,101,016 Gill Aug. 20, 1963 FOREIGN PATENTS 607,961 Canada Nov. 1, 1960 

2. IN ROLLING MILL APPARATUS OF THE TYPE HAVING A PAIR OF WORK ROLLS, AN UNWINDING REEL FOR STRIP MATERIAL TO BE ROLLED BETWEEN THE WORK ROLLS, AND ELECTROMOTIVE MEANS ON THE UNWINDING REEL FOR PRODUCING BACK TENSION IN THE STRIP MATERIAL DURING ROLLING; THE IMPROVEMENT OF GAGE MEANS FOR PRODUCING AN ELECTRICAL SIGNAL WHICH VARIES IN DIRECT PROPORTION TO THE DEVIATION IN THICKNESS OF THE STRIP MATERIAL ENTERING THE WORK ROLLS FROM A PREDETERMINED VALUE, AND MEANS CONNECTED TO SAID GAGE MEANS FOR CONTROLLING THE ELECTROMOTIVE MEANS ON THE UNWINDING REEL WHEREBY THE BACK TENSION WILL VARY IN PROPORTION TO VARIATIONS IN SAID ELECTRICAL SIGNAL. 